Fuse out, but 35v still there?

[J@mes]

Got a lighting circuit in a workshop - there is 235v on it when the fuse is in, but when the fuse is removed it still shows 35 volts on the live side of the switch when the switch is open.

Haven't started taking all the junction boxes apart yet, but has anyone got a starting point to look for?

Thanks

 

[telectrix]

try using an analogue meter for a start. Plenty of 2nd hand AVOs on ebay

 

[J@mes]

Can I ask why that would make any difference? Using a Fluke T-1000 which has recently been calibrated.

Thanks

 

[jeremy]

Check CPC continuity and that there is an earth in the workshop. Sounds like induced voltage which if everything is earthed and bonded properly wont have any welly behind it. This can be checked by removing all energy from the system and doing IR tests between circuits to ensure no shared anything . Hope this helps

 

[J@mes]

There is another lighting circuit which shares junction boxes and the switch box (2 gang grid switch) and the T&E that feeds both circuits does run along for around 10 meters together. Earth is present at the switch box but not tested as I had to leave site before going further in to investigating it.

 

[Sparky Ninja]

There are many things that may need to be investigated here, and unfortunatley you havn't done enough digging yet for us to be of any real help.
Is the fuse the supply fuse, or the circuits fuse?
If you are picking up 35V with the fuse removed from the circuit alone, with other local circuits still energised. You can connect an R2 lead to the point where 35V is being measured, then take the reel to the source and isolate the other circuits one by one till the 35V drops, then you will find the circuit creating the induced voltage.
I had this happen with a shower installation a couple of weeks ago.

 

[telectrix]

still think try analogue meter . if when this shows nothing, then it,s the digi. meter being fooled. don't think i,m being picky but i,m over 50 and know i can trust a needle swinging up the scale.

 

[rocker]

Is it possible that plugged in appliances with capacitors/big coils/flybacks are 'feeding back' unused juice into the system, or is this just so much balls?

 

[alarm man]

have you isolated the main switch and checked its not coming in off the supply neutral

 

[J@mes]

Circuit fuse removed only

all other circuits live

other circuits are more lighting, sockets and a 3 phase saw which was switched off via a rotary isolator but not at the board. Other than the other lighting circuit which was on (and runs alongside the cable run/ shares the switch box) everything else was off - no sockets in use or other loads.

Have a few analogue meters at work so will give them a try too.

Should be going back on Friday, so will try the things mentioned here and see where I get.

Thanks

 

[m4tty]

Defo sounds like induced voltage from other live circuits and agree with telectrix

 

[marksparky]

what about a borrowed neutral from other lighting circuit? just a thought. how about pulling the othe fuses 1 by 1 and test each time u pull a fuse then wen 35v disappear it mite point u in right direction

 

[Had8Lives]

Could be a smoke alarm/emergency light battery back feeding. I've heard of this before.

 

[Sparky Ninja]

Well without any feedback, we will never know

 

[J@mes]

Not had chance to get back up there yet, it's a job for a friend so it's at the bottom of the pile at the minute.

no chance of smoke alarms or emergency lights causing the issue though.

It's either going to be borrowed neutral or inductance due to running for a fair distance with another lighting circuit beside it!